#include <stdio.h>
#define ROWS 3
#define COLS 4
int sum2d(int rows, int cols, int ar[rows][cols]);

int main(void)
{
    int i, j;
    int rs = 3;
    int cs = 10;
    int junk[ROWS][COLS] = {
        {2, 4, 6, 8},
        {3, 5, 7, 9},
        {12, 10, 8, 6}
    };

    int morejunk[ROWS - 1] [COLS + 2] = {
        {20, 30, 40, 50, 60, 70},
        {5, 6, 7, 8, 9, 10}
    };

    int varr[rs][cs];   //变长数组

    for (size_t i = 0; i < rs; i++)
        for (j = 0; j < cs; j++)
            varr[i][j] = i * j + j;

    printf("3x5 array\n");
    printf("Sum of all elements = %d\n", sum2d(ROWS, COLS, junk));

    printf("2x6 array\n");
    printf("Sum of all elements = %d\n", sum2d(ROWS -1, COLS + 2, morejunk));

    printf("3x10 VLA\n");
    printf("Sum of all elements = %d\n", sum2d(rs, cs, varr));

    return 0;
}

// 带变长数组形参得函数
int sum2d(int rows, int cols, int ar[rows][cols])
{
    int r;
    int c;
    int tot = 0;

    for (size_t r = 0; r < rows; r++)
        for (size_t c = 0; c < cols; c++)
            tot += ar[r][c];

    return tot;  
}